Correct documentation for atomic_from_ptr

* Remove duplicate alignment note that mentioned `AtomicBool` with other
  types
* Update safety requirements about when non-atomic operations are
  allowed

library/core/src/sync/atomic.rs

@@ -346,9 +346,12 @@ impl AtomicBool {
     ///
     /// # Safety
     ///
-    /// * `ptr` must be aligned to `align_of::<AtomicBool>()` (note that on some platforms this can be bigger than `align_of::<bool>()`).
+    /// * `ptr` must be aligned to `align_of::<AtomicBool>()` (note that on some platforms this can
+    ///   be bigger than `align_of::<bool>()`).
     /// * `ptr` must be [valid] for both reads and writes for the whole lifetime `'a`.
-    /// * The value behind `ptr` must not be accessed through non-atomic operations for the whole lifetime `'a`.
+    /// * The value behind `ptr` must not be accessed through non-atomic operations whenever
+    ///   the `AtomicBool` is used in a `Sync` context (e.g. read or modified in a different
+    ///   thread).
     ///
     /// [valid]: crate::ptr#safety
     #[unstable(feature = "atomic_from_ptr", issue = "108652")]
@@ -1139,9 +1142,12 @@ impl<T> AtomicPtr<T> {
     ///
     /// # Safety
     ///
-    /// * `ptr` must be aligned to `align_of::<AtomicPtr<T>>()` (note that on some platforms this can be bigger than `align_of::<*mut T>()`).
+    /// * `ptr` must be aligned to `align_of::<AtomicPtr<T>>()` (note that on some platforms this
+    ///   can be bigger than `align_of::<*mut T>()`).
     /// * `ptr` must be [valid] for both reads and writes for the whole lifetime `'a`.
-    /// * The value behind `ptr` must not be accessed through non-atomic operations for the whole lifetime `'a`.
+    /// * The value behind `ptr` must not be accessed through non-atomic operations whenever
+    ///   the `AtomicPtr` is used in a `Sync` context (e.g. read or modified in a different
+    ///   thread).
     ///
     /// [valid]: crate::ptr#safety
     #[unstable(feature = "atomic_from_ptr", issue = "108652")]
@@ -2109,10 +2115,13 @@ macro_rules! atomic_int {
             ///
             /// # Safety
             ///
-            /// * `ptr` must be aligned to `align_of::<AtomicBool>()` (note that on some platforms this can be bigger than `align_of::<bool>()`).
-            #[doc = concat!(" * `ptr` must be aligned to `align_of::<", stringify!($atomic_type), ">()` (note that on some platforms this can be bigger than `align_of::<", stringify!($int_type), ">()`).")]
+            #[doc = concat!(" * `ptr` must be aligned to \
+                `align_of::<", stringify!($atomic_type), ">()` (note that on some platforms this \
+                can be bigger than `align_of::<", stringify!($int_type), ">()`).")]
             /// * `ptr` must be [valid] for both reads and writes for the whole lifetime `'a`.
-            /// * The value behind `ptr` must not be accessed through non-atomic operations for the whole lifetime `'a`.
+            /// * The value behind `ptr` must not be accessed through non-atomic operations whenever the
+            #[doc = concat!("   `", stringify!($atomic_type), "`")]
+            ///    is used in a `Sync` context (e.g. read or modified in a different thread).
             ///
             /// [valid]: crate::ptr#safety
             #[unstable(feature = "atomic_from_ptr", issue = "108652")]